Two main types of shaving aids are known. The first type is water insoluble shaving aids and the second type is water soluble lubricating shaving aids. The water insoluble shaving aids are designed to become slippery when wet without depositing a film on the shaver's skin during wet shaving. On the other hand, the water soluble lubricating shaving aids are designed to deposit a lubricating film on the shaver's skin during wet shaving. Most lubricating shaving aids contain a water soluble component dispersed in a water insoluble matrix.
As used herein, the term "service-life" applies to a lubricating type composite matrix containing at least a water soluble component therein. The term "service-life" refers to the amount of time, sometimes provided as the number of shaves, required to substantially deplete the lubricating water soluble component of the shaving aid from the water insoluble matrix during wet shaving. Substantial depletion of the water soluble component of the shaving aid typically exposes the rough water insoluble matrix and further causes the surface of the shaving aid to become both irregular and rough, thereby, increasing its coefficient of friction when drawn over a shaver's skin, thus, presenting a source of skin irritation during wet shaving.
In wet-shaving razor systems, there are several factors which can contribute to discomfort during shaving. Such factors include, but are not limited to, excessive frictional drag of the razor across the skin, the force needed to cut the hair which depends on, among other things, the mechanical strength of the hair protein structure and degree of clogging of the razor parts with whisker, skin and other debris. Other detracting factors include various skin conditions such as eczema, psoriasis, other rashes, erythema (redness), acne, other skin eruptions and previously inflicted nicks and cuts.
Efforts to remedy at least some of these noted problems have included the use of pre-shave and after-shave lotions, special whisker-softening lathers or agents, blood coagulants and other medicinal or soothing bio-effecting agents. Various agents, namely, shaving foams, shaving soaps, stubble softening agents as well as medicinal or cosmetic substances or combinations of all these have been used. Such shaving agents reduce either the cutting work which has to be done to separate the stubble by softening the stubble or act as a lubricant which reduces the frictional force between the various parts of the shaving razor in contact with the shaver's skin. Even though shaving comfort can, to some degree, be enhanced by the use of one or more of the above-mentioned agents, the requirement that they be applied before or after shaving (because of loss due to evaporation or repeated shaving strokes) lessens their effectiveness.
In view of these problems, it is believed that a shaving aid integrally included with or attached to the shaving instrument itself will provide improved shaving features. For example, lubricating shaving aids integrated with or attached to the shaving instrument itself will substantially reduce the frictional drag of the razor blade(s) as the razor is drawn across the shaver's skin. Frictional drag is substantially reduced by simultaneously lubricating the skin during the act of wet shaving.
It was proposed to fit a strip of water insoluble polystyrene and a water soluble lubricant such as polyethylene oxide in a recess on the cap of a razor. The endeavor was to continuously dissolve out the water soluble polymer components during the course of the wet shave and to produce a lubricating film on the skin. This was expected to reduce friction between the skin and the shaving razor during shaving and to make shaving softer and more comfortable.
To that end, U.S. Pat. No. 4,170,821 to Booth discloses a lubricating shaving aid (attached to a disposable razor blade cartridge) which dissolves out a water soluble lubricant during the act of wet shaving. The lubricant, as part of the shaving aid, was incorporated into a matrix of water insoluble polystyrene. According to Booth, the shaving aid can contain a water soluble lubricating oil such as microencapsulated silicone oil; water soluble polyethylene oxide; non-ionic polyacrylamide; and/or a natural polysaccharide derived from plant materials, e.g., guar gum; a depilatory agent; a medicinal agent for killing bacteria or repairing skin condition; a cosmetic agent for softening the skin; or a blood coagulant.
However, there are some disadvantages recognized in the art to using shaving aids such as those described by Booth '821. The water soluble lubricant dissolves or leaches out of the water insoluble matrix during wet shaving, leaving behind the depleted water insoluble matrix. Typically, when the water soluble component of the shaving aid is nearly depleted, the lubricating shaving aid is at the end of its service life. It has been reported in U.S. Pat. No. 4,872,263 to Ethredge, III, that the shaving aid of Booth suffers from certain disadvantages including a service-life lasting on the average of three shaves. Thereafter, its surface becomes irregular and rough and its coefficient of friction increases, contributing to further skin irritation with continued use. At this stage, only a slight amount of lubricant may be provided, if any, by the shaving aid. It is at this point, when the cutting action and shaving comfort of the razor blade have deteriorated through wear that the additional lubricant effect is needed. However, due to the Booth shaving aid's relative short service life, an adequate quantity of lubricant is no longer available.
As opposed to lubricating shaving aids, water insoluble xerogels of polyvinyl pyrrolidone and polyurethane were developed as disclosed, for example, in U.S. Pat. No. 5,056,221 to Theone. Upon exposure to water during wet shaving, xerogels swell into lyogels which are more slidable on the shaver's skin than in their dry xerogel state. The colloidal substance forming the lyogel does not, however, pass into solution, and consequently, does not provide a lubricating film on the shaver's skin during wet shaving. Other water insoluble shaving aids include hydrogels (e.g., polyvinyl pyrrolidone/polyurethane hydrogels of U.S. Pat. No. 4,875,287 to Creasy et al.), interpolymers (e.g., polyvinyl pyrrolidone/polyurethane interpolymers of U.S. Pat. No. 5,005,287 to Riter) and the like.
Though lubricant depletion is not encountered with water insoluble shaving aids, it is preferred to provide a lubricating shaving aid for greater shaving comfort. It is further preferred to provide a shaving aid having a slow dissolution rate for increasing the shaving aid's service life and for greater wet shaving comfort. Slow dissolution rates prolong the service life of the lubricating shaving aid and delay the leaching out of all (or nearly all) of the shaving aid lubricant.
It is further desirable to provide a lubricating shaving aid that deposits a film of both the water soluble polymer component thereof and the water insoluble polymer component thereof on a shaver's skin during wet shaving for greater shaving comfort and to provide a method for making the same.
It is additionally desirable to provide a lubricating shaving aid that deposits a film of both the water soluble polymer component thereof and the water insoluble component thereof wherein the latter component is gradually and uniformly released without imparting a rough surf ace to the shaving aid, thereby maintaining a low coefficient of friction and a smooth profile.